To reduce the bulk of high-tension units while ensuring safety, the electrical apparatus is often installed in metal casings filled with an insulating gas at low pressure, e.g. sulphur hexafluoride or a mixture of sulphur hexafluoride with nitrogen or any other gas having good dielectric properties. This is particularly true of sets of bars whose components are disposed longitudinally end to end and coaxially in metal casings which are generally radially symmetrical so as to obtain uniform electric fields. When the unit is installed in situ, the various components are installed in order, one after another. However, when a given component is to be handled, it is important to be able to remove only the component concerned without being obliged to remove the neighbouring components. Now, although this is relatively easy for parallel-connected components, it is not so easy when said components are disposed in series, end to end, as in the case of sets of bars.